1. Field of the Invention
The present invention relates to a method of producing a semiconductor device having resin bumps, that serve as external connection terminals, formed integrally with a resin-sealed portion that seals a semiconductor chip, and a metal substrate applicable to the same.
2. Description of the Related Art
FIG. 1 is a sectional view showing a semiconductor device having external connection terminals formed by means of resin bumps that are formed integrally with a resin-sealed portion. In the drawing, reference numeral 10 denotes a semiconductor chip, 12 denotes a resin-sealed portion and 14 denotes an external connection terminal. The external connection terminals 14 are formed by providing metal films 18 to coat the resin bumps 16 formed to protrude from the bottom face of the resin-sealed portion 12 on the chip mounting face of the semiconductor device. Electrodes of the semiconductor chip 10 and the metal films 18 are electrically connected via bonding wires 20. Reference numeral 22 denotes a resin that protects the back face of the semiconductor chip by preventing the bottom face of the semiconductor chip 10 from being exposed from the resin-sealed portion 12.
FIG. 2 is a bottom view of the semiconductor device. The external connection terminals 14 are arranged at positions that surround the semiconductor chip 10, with the metal film 18 of each of the external connection terminals 14 being electrically connected to the electrode of the semiconductor chip 10 by wire-bonding. When the semiconductor chip 10 and the metal film 18 of the external connection terminals 14 are connected directly with the bonding wire 20, a wiring pattern for electrically connecting the external connection terminals and the bonding wires becomes unnecessary, and it is also unnecessary to secure a space for providing the wiring pattern, thus making it possible to reduce the size of the semiconductor device.
FIG. 3(a) to FIG. 3(e) show the method of producing the semiconductor device described above. First, a photo-resist is applied to the surface of a metal substrate 30 such as copper foil, exposed to light and developed, thereby to form a photo-resist pattern 32 with openings where the external connection terminals 14 are to be formed (FIG. 3(a)). Then the metal substrate 30 is half-etched using the photo-resist pattern 32 as a mask to form a recess 34 (FIG. 3(b)). The inner surface of the recess 34 is then coated with plating of palladium or the like to form a metal film 18 (FIG. 3(c)). Then the semiconductor chip 10 is mounted on the metal substrate 30 via the chip fastening resin 22, and the electrodes of the semiconductor chip 10 and the metal films 18 formed on the bottom faces of the recesses 34 are connected by wire-bonding (FIG. 3(d)).
Then one side of the metal substrate 30 whereon the semiconductor chip 10 is mounted is sealed with a resin by a resin sealing apparatus. FIG. 3(e) shows the condition of the semiconductor chip 10 sealed with the resin. The semiconductor device is obtained by dissolving and removing the metal substrate 30 by etching the semiconductor chip 10 sealed with the resin. There is another method of producing the semiconductor device in which the metal films 18, the resin-sealed portion 12 and the like are formed in such a way as can be exfoliated from the metal substrate 30, and the resin-sealed portion 12 is exfoliated from the metal substrate 30 thereby separating them after sealing with the resin.
The semiconductor device described above is characterized by the fact that the semiconductor device can be provided as a small size product. However, because the resin bump 16 is formed integrally with the resin-sealed portion 12 when sealed with the resin, it is necessary to form the recess 34 in the metal substrate 30. Also because the bottom face of the recess 34 serves as a bonding pad, an area necessary for bonding must be secured on the bottom face of the recess 34, thus making it impossible to arrange the external connection terminals 14 in a high density.
FIG. 4(a) and FIG. 4(b) are enlarged views of the arrangement of the connections between the external connection terminals 14 and the mounting substrate. In the semiconductor device of the prior art, a bonding pad for connecting the external connection terminals 14 to the mounting substrate is a rectangle measuring about 0.6.times.0.3 mm, with intervals of about 0.65 mm between terminals. The bonding pad for connecting the external connection terminal 14 has a rectangular shape because a certain amount of area is required for the bonding pad and because the bottom face of the recess 34 is required to have a certain amount of area in order to prevent a bonding tool or the bonding wire 20 from making contact with an edge of the recess 34 when the bonding tool advances toward the bottom face of the recess 34. The recess 34 is also required to have a depth of about 0.3 mm in order to ensure the height of the external connection terminals 14.
When a product having a multitude of pins is produced with the semiconductor device having resin bumps 16 that serve as external connection terminals 14 being formed integrally with the resin-sealed portion 12 that seals the semiconductor chip, layout of the external connection terminals 14 is limited in the connecting construction of the prior art, and it is difficult to effectively mount with high density.